The present invention relates in general to the control of three-phase inverters used to supply electrical power from a generic electrical power source to a three-phase grid, to which a load with known characteristics may be applied. More specifically, the present invention relates to a method and to a device for regulating an inverter in parallel to the grid.
In the use of renewable energies and more generally alternative energies, it is frequently necessary to transfer power generated by a generic source to a three-phase electrical grid. For example, it may be necessary to transfer the electrical power obtained from a fuel cell generator, or from a photovoltaic solar panel, to a three-phase grid. The characteristics of the generator vary greatly, for example as a function of environmental conditions (in the case of photovoltaic solar panels). Therefore, the problem arises of transferring electrical power in the form of current, with non-constant characteristics, to a grid with an alternating voltage with precise and constant characteristics.
Transfer of electrical power typically takes place through an inverter, which is controlled by a pulse-width modulated (PWM) signal so as to supply the three phases of the grid with currents suitably synchronized with the phase voltages. In order to synchronize the output current of the inverter with the grid voltage, “Phase Locked Loop” (PLL) control algorithms have been used. These algorithms have some drawbacks and limits.